ply support

Former-commit-id: ec7e5380973a193b1fdb7d2a9541b83b7e50cfcb

examples/patches/example.cpp

@@ -1,4 +1,5 @@
 #include <igl/readOBJ.h>
+#include <igl/readPLY.h>
 #include <igl/writeOBJ.h>
 #include <igl/writeOFF.h>
 #include <igl/readWRL.h>
@@ -750,6 +751,13 @@ int main(int argc, char * argv[])
     {
       return 1;
     }
+  }else if(ext == "ply")
+  {
+    // Convert extension to lower case
+    if(!igl::readPLY(filename,vV,vF,vN,vTC))
+    {
+      return 1;
+    }
   }else if(ext == "wrl")
   {
     // Convert extension to lower case